1. Field of the Invention:
This invention relates to an apparatus used to position a floating vessel so as to place the bow of the vessel into the direction of approaching waves. Orientation of the vessel in this manner reduces the risk of the vessel capsizing, reduces discomfort, fatigue, and risk of injury to the crew, and reduces the wave drift forces tending to move the vessel off location if the vessel is moored with multiple anchors or by dynamic positioning.
2. Description of the Prior Art:
In a storm when waves become high enough even large vessels must turn the bow into oncoming waves to reduce the risk of damage and the possibility of capsizing. This is true of vessels traveling at sea from one point to another. It is also true with vessels moored on a location such as drilling vessels because with drilling vessels it is important even in lower sea states to point into the waves to reduce lateral movements of the vessel which cause much discomfort, fatigue, and hazard to the crew involved in the drilling operation.
Waves that impact a vessel at any angle except directly on the bow or stern cause lateral components of acceleration and vessel motion from yaw, sway, and roll. This lateral motion makes manual work most difficult; workers must brace themselves strongly and move with the vessel or walk from side to side to stay upright. Objects that are tied down strain their lashings and slide or roll and become dangerous if they break free. This lateral motion hampers crew operations, especially on vessels where manual labor must continue during adverse weather conditions, such as when an offshore drilling vessel is positioned over subsea wellheads.
In an attempt to reduce this lateral motion a system to turn a vessel into the waves was installed for use on a dynamically positioned vessel in 1980. The system would turn the vessel to port a few degrees, and then by monitoring an inclinometer measure any change in the magnitude of the roll angle of the vessel. If the roll angle decreased, the vessel was turned to port another increment. If the roll angle increased, the vessel was turned to starboard. This process was continued until the roll angle had decreased to a minimum, at which time the vessel would maintain this general heading, while still arbitrarily searching to port or starboard in an attempt to maintain the roll rate of the vessel at a minimum.
The arbitrary heading changes of the vessel as this system attempted to point the vessel into the waves was not well received by the crew of the vessel and the system was subsequently removed from operation.
A simpler apparatus was discovered Jan. 31, 1984, comprising a mass elastically suspended visually in front of the vessel's helmsman. The suspended mass duplicates the motion and direction of the wave particles which form the waves that impact the vessel, thereby informing the helmsman what heading the waves have relative to the vessel and thereby what direction to turn the vessel to head into the oncoming waves. Such a device is the object of the related patent application Ser. No. 692,094, now U.S. Pat. No. 4,633,710, entitled "Ship Wave Heading Indication Method and Apparatus" by Howard L. Shatto, Jr., filed Jan. 17, 1985.
The device, however, requires continuous monitoring by the helmsman at a time during foul weather conditions when his attention may be required elsewhere.
A system need be disclosed, therefore, that provides the operator a continuous indication of the wave direction and which can operate automatically to maintain the vessel turned into oncoming waves without the help of a helmsman and without the requirement of continuous change of the vessel heading in order to locate the minimum roll rate of the vessel. Such an apparatus should automatically determine what direction the vessel should be turned in order to reduce lateral motions and to minimize the risk of capsize of the vessel.